Our Cultural institutions Page highlights our ongoing support of museums and cultural institutions with free accounts and access to tools. In Cultural Heritage Spotlight, we’ll explore museums and cultural institutions who are using 3D technology to bring new life to their collections. Today’s blog post features Thunder Bay National Marine Sanctuary, who conducts, supports, promotes, and coordinates scientific research and monitoring of its maritime heritage resources to ensure their long-term protection. Thunder Bay National Marine Sanctuary is managed jointly by NOAA and the state of Michigan.
Located in northwestern Lake Huron, Thunder Bay National Marine Sanctuary is adjacent to one of the most treacherous shipping lanes within the Great Lakes system. Unpredictable weather, murky fog banks, sudden gales, and rocky shoals earned the area the name “Shipwreck Alley.” Today, a 4,300-square-mile National Marine Sanctuary protects one of America’s best-preserved and nationally-significant collections of shipwrecks. Fire, ice, collisions, and storms have claimed over 200 vessels in and around Thunder Bay. To date, nearly 100 shipwrecks have been discovered within the sanctuary. Although the sheer number of shipwrecks is impressive, it is the range of vessel types located in the sanctuary that makes the collection so significant. From an 1838 side-wheel steamer to a modern 500-foot-long German ocean-going freighter, the shipwrecks of Thunder Bay represent the microcosm of maritime commerce across the Great Lakes.
Northeastern Michigan’s maritime landscape includes hundreds of shipwrecks located on Lake Huron bottomlands. It also encompasses all of the cultural and natural features related to maritime heritage. Lifesaving stations, lighthouses, historic boats and ships, commercial fishing camps, docks, and working ports are among the more obvious historic and archaeological features. Many features are less visible and some remain unrecognized or unknown.
Documenting, monitoring, and interpreting many of these shipwreck sites is challenging, especially those located in deep waters beyond the reach of conventional scuba diving practices. Recently, sanctuary archaeologists have begun using photogrammetric surveys to quickly assess individual sites. Never before have we been able to visualize, understand, and interpret a site with a data product that can be collected in a 30-minute dive. Below is a 3D model of the canal schooner Kyle Spangler which sunk in 185 feet of water after a collision with another vessel in 1860. In 2008, sanctuary archaeologists and citizen scientists mapped the site using tape measures and slates. The initial documentation survey took 55 dives, while a photogrammetry exercise carried out in 2015.
To achieve complete site coverage, archaeologists swim pre-planned paths around the shipwreck and capture images at 60% overlap. These flight paths typically begin around the deepest (water depth) contour and spiral upwards towards the surface, circumnavigating the shipwreck. Complete outboard hull passes are prioritized followed by overhead passes, and artifact-specific photo acquisitions.
When captured with 60% overlap coverage at consistent aperture, shutter, and ISO settings, these photo acquisition strategies have proved effective at generating complete 3D models via Agisoft Photoscan software. Our full site models have been produced with between 800 and 1200 photographs shot with a Nikon D4 and D800. The 1863 wooden passenger/package freight propeller Pewabic, for example, required 1187 photographs to properly generate full site point cloud data largely due to its massive and detailed centerline arch. This structural member is anchored to the keelson and prevented the 200’ wooden hull from hogging and sagging (aka drooping) at bow and stern. Other factors that affect clean photograph acquisition include water clarity, ambient light, and distance to target.
In addition to the added capacity that photogrammetry offers our archaeological needs, 3D models’ interactivity offers an unparalleled virtual experience to our public audience. The Great Lakes Maritime Heritage Center in Alpena, Michigan is Thunder Bay’s visitor center complete with full-size canal schooner replica, 93 seat high definition theatre, interactive exhibits, and the “Science on a Sphere®” pictured below.
The Science on a Sphere ® is a global display system that uses four projectors to seamlessly project planetary data onto a 6-foot diameter hanging sphere. Imagine using a tablet with pre-loaded models and taking a virtual dive to the depths of Thunder Bay! The Science on a Sphere® is one of several dynamic platforms to begin integration of 3D models into our exhibits.
Perhaps the most exciting prospect for 3D model generation in the sanctuary is the utilization of local, regional, and national citizen science organizations to help Thunder Bay image every shipwreck in the sanctuary. Many groups who have previously worked in the sanctuary like the National Association of Black Scuba Divers (NABS), East Carolina University’s Program in Maritime Studies, and the Noble Odyssey Foundation have experience in photogrammetry or can build capacity to assist in data collection. Photogrammetry offers the sanctuary yet another avenue to interface and collaborate with these active dive groups to expand our inventory of sites and encourage stewardship of these incredible submerged cultural resources in Thunder Bay.
In sum, Thunder Bay National Marine Sanctuary and similar maritime heritage institutions are constantly exploring new technologies to better understand, interpret, and share the cultural resources we help protect. Photogrammetry is one tool that will better connect archaeologists, educators, and the public with these fascinating resources from our shared maritime past.
Thanks again for sharing, Phil!
For more information on the sanctuary, visit thunderbay.noaa.gov and check us out on Facebook at https://www.facebook.com/thunderbayshipwrecks.
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